1. Field of the Invention
The present invention relates to an encoder combined with a magnetic sensor and used for detecting a rotating speed, an angle of rotation and the like of a rotating part such as a rotating shaft or the like.
2. Description of the Conventional Art
Conventionally, as shown in FIG. 8, there has been known an encoder 51 in which N poles 52 and S poles 53 of magnets are arranged alternately in a circumferential direction at an equal pitch. Further, for example, in the encoder 51 for an engine in which it is necessary to specify an angle of rotation of the rotating shaft, in order to specify a rotational position thereof, an unequal pitch portion 54 forming a reference point on the circumference is provided in a part on the circumference.
However, in conventional, since the encoder 51 is manufactured by using a magnetizing head having a special shape provided with the unequal pitch portion in a part on the circumference of a magnetism applying portion, for forming the unequal pitch portion 54 in the encoder 51, the magnetizing head is exclusively used, so that there is a disadvantage that it is necessary to manufacture the magnetizing head per item of the encoder 51. The magnetizing head having the special shape provided with the unequal pitch portion mentioned above has a complicated shape and is expensive.
Further, as another conventional art of the present invention, Japanese Unexamined Patent Publication No. 2003-270258 describes an encoder (a pulsar ring) which is constituted by an annular support member and at least one band-shaped magnetizing body attached along a peripheral direction of the annular support member, and in which mutually facing end magnetic poles of the magnetizing body are set to be the same pole and a gap is formed in confronted portion of the magnetizing bodies, whereby a detected portion for a reference position signal having a small bottom value existing a peak portion of an output signal is formed at least one position on a circumference of the ring. However, the conventional art described in this publication also necessary to use the magnetizing head having the special shape provided with the unequal pitch portion.